1. Field of the Invention
This invention relates to ankle prostheses and the surgical procedures for implanting such prostheses.
2. Description of Prior Art
For many years there has been considerable interest and activity with respect to ankle joint replacements, in which the degenerative articular surfaces are removed and replaced with an artificial joint called a prosthesis, as a viable approach to the treatment of diseased or injured ankle joints.
Fusion has long been an alternative to ankle arthroplasty. This approach has its drawbacks. For example, there is a loss of motion in the ankle joint which may cause difficulties with other associated parts of the foot and leg.
Many types of ankle joint prostheses have been developed over the past thirty years. After initial encouraging results, the reputation of ankle arthroplasty was somewhat damaged based on long-term, follow-up clinical studies which revealed the frequent failures of such implants due mainly to the inadequate restoration of the original mobility and the poor stability of the resulting ankle complex. Problems which many have speculated are due to our poor understanding of the relative contribution of the ligamentous structures and articular surfaces in providing passive and active stability for the ankle joint.
The ongoing problems with ankle arthrodesis have encouraged numerous ankle arthroplasty designs. The early designs all feature two-component prostheses having talar and tibial components for respective attachment to the talar and tibia bones of the ankle. For example, see U.S. Pat. Nos. 4,156,944, 4,069,518, 4,021,864, 3,987,500, 3,975,778, 3,896,503, 3,896, 502, 3,889,300, 3,86,599, 3,872,519 and 3,839,742.
Despite the multitude of these designs, none of them yielded clinical results comparable to those achieved with total hip and knee replacement surgeries. Aseptic loosening of the tibial and/or talar components is reportedly the most frequent cause of failure, but complications also included deep infections, dehiscence of the surgical wound, lateral and/or medial subluxation of the floating meniscus and lateral talofibular joint impingement.
The most recent prosthesis design feature three components and include a floating, intermediate element that has been introduced to allow full congruence at the articular surfaces in all joint positions in order to minimize wear of the components while coping with the multi-axial nature of the axial rotation of the ankle. These designs all feature a planar and a curved surface for the intermediate element in order to allow a controlled freedom of motion relative to the tibial component, allowing controlled anterior-posterior as well as medial-lateral motion in such a way as to reduce wear of the surfaces and the stress at the interface between the bone and the tibial component of the prosthesis. For example, see U.S. Pat. Nos. 4,470,158, 4,755,259 and 5,766,259. These three component designs are also reported to have exhibited problems with aseptic loosening of the tibial and/or talar components, migration of the prosthesis and inadequate motion in the replaced joint.
A common characteristic among these previous total ankle prostheses is that they are inserted through incisions made with an anterior approach to the ankle joint. This approach requires making large incisions at the ankle and moving the tendons and other soft tissue aside; thus violating important anterior soft-tissue structures and, more importantly, neurovascular structures that provide blood flow to the talus.
Despite the extensive development of ankle joint prostheses, they often continue to exhibit less than desirable performance. Thus, there exists a continuing need for the development of new and improved types of such devices. There is also a need for a less invasive surgical method to install such a prostheses so as to yield improved healing and a decrease in the failure rate of such devices.
3. Objects and Advantages
There has been summarized above, rather broadly, the prior art that is related to the present invention in order that the context of the present invention may be better understood and appreciated. In this regard, it is instructive to also consider the objects and advantages of the present invention.
It is an object of the present invention to provide an improved ankle joint prosthesis that decreases the failure rate currently being experienced by such devices.
It is another object of the present invention to provide a less invasive surgical method for inserting an ankle joint prosthesis so as to yield improved healing and a decrease in the failure rate of such devices.
It is yet another object of the present invention to provide a surgical method that utilizes a lateral approach, as opposed to the standard anterior approach, for inserting an ankle joint prosthesis.
It is a further object of the present invention to provide a surgical method for implanting ankle joint prostheses that utilizes a lateral approach, as opposed to the standard anterior approach, so as to preserve the blood supply to the talus, thereby avoiding the avascular pathologies known to be caused by damaging the blood supply to the talus.
It is an object of the present invention to prepare the ankle joint for the insertion of an ankle joint prosthesis using a crescentic shaped saw, which allows for minimum bone resection that follows the natural contours of the joint and preserves the strongest portion of the distal tibia and talus for implantation of an ankle prosthesis.
It is an object of the present invention to provide an ankle joint prosthesis having components that have crescentic shaped surfaces for attachment with the adjoining tibia and talus bones so as to provide more surface area for bony ingrowth or cement fixation than that provided by standard prostheses which use flat surfaces.
It is an object of the present invention to present an ankle joint prosthesis with different levels of constraint, ranging from unconstrained to semi-constrained. This provides options for dealing with different clinical situations. Ultimately, the goal will be to use an ankle joint prosthesis, which minimizes wear and enhances the longevity of the implant.
It is a still further object of the present invention to provide a device and method that will advance the effectiveness of ankle joint replacements in orthopedic medicine.
These and other objects and advantages of the present invention will become readily apparent as the invention is better understood by reference to the accompanying summary, drawings and the detailed description that follows.